"Mouse" computer input devices were invented in the 1970s to improve the interface between man and machines. Such mouse input devices allow a user to control a position of a cursor or pointer on a computer screen and enable user input to a computer based upon the position of the cursor, without the use of keys on a conventional keyboard. This type of peripheral device was well-suited for the newly developed "point-and-click" graphical user interface format of software. Generally, all mouse cursor control devices require some sort of planar surface such as, for example, a desktop or mouse pad, for proper operation. This requirement is disadvantageous because it physically restrains a user to remain very near the computer, monitor, or work station, in order to control the mouse. This confined proximity can produce several undesirable effects such as, for example, eye strain from sitting too close to a computer display and arm fatigue from having to continuously extend a hand out to reach the mouse on the planar surface.
As alternatives to the mouse, other types of cursor control devices have been developed such as, for example, "track-ball" type cursor controllers, the GlidePoint.RTM. manufactured by Cirque Corp. of Salt Lake City, Utah, and the TrackPoint.RTM. manufactured by IBM Corp. of Armonk N.Y. The track-ball type of cursor controller allows a user to rotate a ball in various directions to directly move a cursor on the screen. Many track-ball controllers, however, suffer from an undesirable effect: the high degree of freedom of rotation of the track-ball within its mounting socket makes accurate control of cursor position somewhat difficult. This can be particularly frustrating to a user where accurate control of a cursor is required, such as in computer-aided drafting and other graphical applications. This undesirable effect is present whether the track-ball controller is mounted within a keyboard, incorporated into a hand-held unit, or exists as a table mounted stand-alone unit. Additionally, the mechanical components of track-ball type controllers do not lend themselves to miniaturization where space and weight considerations are very important. The GlidePoint.RTM. controller includes a capacitance sensitive planar pad which detects the presence of a human finger thereon. Since a planar pad is required for detecting and tracking the motion of a user's finger thereon, the GlidePoint.RTM. also suffers from the disadvantage of not being amenable to miniaturization for "space-saving" applications. The TrackPoint.RTM. is a small, light, force-sensing stick assembly which is typically incorporated into a keyboard, between the G, H and B keys. In essence, a user merely pushes against the TrackPoint.RTM. to move a cursor in a desired direction. However, because the device is in the keyboard, it continues to restrain the user to be within reach of the keyboard in order to point, click, drag, draw, or perform any other cursor or pointer related operations.
Weight and "space-saving" considerations are very important when incorporating cursor control devices into computer systems such as, for example, laptop or notebook computers. Accordingly, "space-saving" circuit board designs reduce or make available additional valuable space in computer systems. However, the nature of most cursor control circuitry is such that low-level analog signals are produced. This particularly true for TrackPoint.RTM. type controllers. Accordingly, certain precautions such as, for example, the avoidance of digital signal "pickup" into analog circuits, must be considered when designing a "space-saving" circuit board design. Therefore, a small, highly compact, "space-saving" circuit board design which does not intrude on the limited space of a computer system and provides the required electrical isolation from the noise generated by central processing units (CPU's), video lines, buses, or any other digital signal sources, is highly desirable.